Q. What are the advantages and disadvantages of using a product like Shiva Casein Varnish? Are there any other casein varnishes that are good?Craig KlafetaRolling Meadows, IL

A. First, I assume youre using the varnish only with casein paints, since thats what the product is made for; it shouldnt be used with any other kinds of paints such as watercolors, acrylics or oils. Although its fashionable to mix media, youll risk making a physically vulnerable and unstable painting. If you do mix your media, use one dominant paint material, with perhaps one or two secondary materials scattered throughout the picture. Of course, this is a “rule” that begs loudly to be broken, and its so often ignored that painting conservators are assured of lifetime employment.

Second, if youre using this product to varnish a finished casein painting, that would be an acceptable use, but its unnecessary. Casein paintings are meant to have a matte, not a glossy, surface, and can be protected by framing behind glass.

If youre using the casein varnish like a medium, mixing it into the paints as you apply them, then remember that if a product label describes the materials use, its not meant to be used in any other way. So, if the product label says “varnish” then the product is meant to be used as a final coating, not as a medium. However, you could use the product as part of a medium, as long as the use isnt excessive (I wouldnt add more than 10 percent of the varnish, by volume, to a mixture of color). Even though casein is relatively insoluble once its dry, you can run the risk of producing more fragile paint layers if you use too much of the varnish. If youre trying to increase the gloss of the paints, again remember that casein paints arent glossy paints.

Finally, as to your second question, I know of no casein products on the market other than Shivas.

Mark Gottsegen is an associate professor of art at the University of North Carolina at Greensboro.